1. Technical Field
The invention relates to plasma processing. More particularly, the invention relates to a plasma etch process for controlling the profile of an etched sidewall.
2. Description of the Prior Art
Plasma processing is an essential tool of the semiconductor manufacturing industry. In a plasma etch process, electromagnetic radiation is used to dissociate the molecules of process gas to produce a reactive species. i.e. a plasma. The plasma is directed to the surface of a workpiece, such as a semiconductor wafer, in a process environment, typically a vacuum chamber. The wafer is masked with a photoresist material to define a circuit pattern. The plasma etches openings into unmasked portions of the wafer. The slope or profile of these openings varies according to the choice of plasma precursor process gases. Thus, an isotropic process etches equally in all directions, while an anisotropic process etches primarily in one direction. For example, processes such as reactive ion etch ("RIE") permit the anisotropic etching of small openings having high aspect ratios. Smaller device features may thereby be produced.
FIG. 1 illustrates a typical RIE apparatus, according to the prior art. A wafer support 12 is located within the process chamber 10. The wafer support is connected to a radio frequency ("RF") power source 14 and serves as a cathode. The walls 16 and base 18 of the chamber form the grounded anode of the system.
Gas supplied to the chamber through an inlet port 20 passes through a gas distribution plate 22 and is directed to the surface of the workpiece 24. The RF energy supplied to the process chamber dissociates the molecules of the process as to produce a reactive species that is used to etch the workpiece.
Alternately, the plasma may be remotely generated in an applicator 26 by application of a microwave ("MW") or RF power source 28. The remotely generated plasma is then ported to the process chamber. An anisotropic etch is achieved as the amount of RF energy supplied to the electrodes is increased. The spent process gas is then exhausted from the process chamber through an outlet port 30 by a vacuum pump 32.
It is often desirable to control the profile of the sidewalls of the etched opening. For example, sloped sidewalls are desired when an opening is made in a dielectric layer, such as silicon oxide, for the deposition of metal. It is known to use various etchant mixtures to produce sloped sidewalls. However, such processes are generally difficult to control, such that the resulting openings are non-uniform. Further, it is difficult to provide smaller interlayer and active element contact regions than the corresponding feature size on the overlying photoresist layer. Rather, the etch process tends to etch under the photoresist, thereby producing an opening having a larger diameter than that of the masked region of the wafer.
It would therefore be advantageous to provide a process for controlling the profiles of sidewalls formed when etching a workpiece. It would be a further advantage if such process provided smaller interlayer and active element contact regions than the corresponding feature size on the overlying photoresist layer.